Magnetic nerve stimulation seat device

ABSTRACT

A magnetic nerve stimulator system is comprised of a core constructed from a material having a high field saturation with a coil winding. A thyrister capacitive discharge circuit pulses the device. A rapidly changing magnetic field is guided by the core, preferably vanadium permendur. For task specific excitation of various nerve groups, specially constructed cores allow for excitation of nerves at deeper levels with higher efficiency than is possible with air-core stimulators. Among the applications possible with this invention are treatment of incontinence, rehabilitation of large muscle groups in the leg and arm, and excitation of abdominal wall muscle groups to aid in weight loss and metabolic rate increase. A C-shape is employed for focussing the stimulation as desired.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 09/001,782 filed Dec. 31, 1997, now U.S. Pat. No. 6,086,525,which is a continuation-in-part of U.S. patent application Ser. No.08/345,572, filed Nov. 28, 1994 (patented and issued as U.S. Pat. No.5,725,471). The present application is also a continuation-in-part ofU.S. patent application Ser. No. 09/125,646 filed Mar. 15, 1999, nowU.S. Pat. No. 6,132,361, which claims priority to PCT Application Ser.No. PCT/US97/14826 filed Aug. 15, 1997, which claims priority to U.S.Provisional Application Ser. No. 60/023,421 filed Aug. 15, 1996. Allrights of priority are claimed to those prior applications, thedisclosures of which are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART

A nerve cell can be excited in a number of different ways, but onedirect method is to increase the electrical charge within the nerve,thus increasing the membrane potential inside the nerve with respect tothe surrounding extracellular fluid. One class of devices that fallsunder the umbrella of Functional Electrical Stimulation (FES) realizesthe excitation of the nerves by directly injecting charges into thenerves via electrodes which are either placed on the skin or in vivonext to the nerve group of interest. The electric fields necessary forthe charge transfer are simply impressed via the wires of theelectrodes.

FES is accomplished through a mechanism which involves a half-cellreaction. Electrons flow in wires and ions flow in the body. At theelectro-electrolytic interface, a half-cell reaction occurs toaccomplish the electron-ion interchange. Unless this half-cell reactionis maintained in the reversible regime, necrosis will result—partiallybecause of the oxidation of the half-cell reaction and partially becauseof the chemical imbalance accompanied by it.

The advantage of FES is that the stimulation can usually be accomplishedfrom extremely small electrodes with very modest current and voltagelevels. The disadvantage however, is that it involves half-cellreactions. Most rehabilitation programs using FES place the electrodesdirectly on the skin. A conductive gel or buffering solution must be inplace between the electrodes and the skin surface. Long term excitationof nerve or muscle tissue is often accompanied by skin irritation due tothe current concentration at the electrode/skin interface. This problemis especially aggravated when larger excitation levels are required formore complete stimulation or recruitment of the nerve group.

By contrast, magnetic stimulation realizes the electric fields necessaryfor the charge transfer by induction. Rapidly changing magnetic fieldsinduce electric fields in the biological tissue; when properly oriented,and when the proper magnitude is achieved, the magnetically inducedelectric field accomplishes the same result as realized by FES, that oftransferring charge directly into the nerve to be excited. When thelocalized membrane potential inside the nerve rises with respect to itsnormal negative ambient level of approximately −90 millivolts (thislevel being sensitive to the type of nerve and local pH of thesurrounding tissue), the nerve “fires.”

The present invention is especially targeted at applications that arenot suited for the use of implanted electrodes. The invention isdesigned for non-invasive external stimulation of selected nerve ornerve groups, particularly in certain applications. In theseapplications, which include incontinence and rehabilitation of musclegroups as well as potential weight loss treatment, the desiredexcitation levels using FES often fall outside of what might beconsidered comfortable limits. That is, the electrical current thatideally would be injected through the skin to excite the muscle groupsof interest often leads to some skin irritation with time. The inventioncan also be used even in applications where this is not the case, as theuse of gels and direct electrode/skin placement is inconvenient and isoften resisted by the patient.

As opposed to FES, magnetic excitation has the attractive feature of notrequiring electrode skin contact. Thus, stimulation can be achievedthrough the clothing that is being worn. This overcomes the objection ofinconvenience and preserves the patient's dignity. Secondly, becausethere is no direct contact, stronger excitation levels can be realizedwithout undue additional skin irritation. A contribution offered by thepresent invention is the ability to achieve higher levels of focusing ofthe magnetic field and thus stimulation within the patient. Commensuratewith this greater level of focusing comes some flexibility in the numberof possible applications that might be targeted. Also accompanying thefocusing is a higher level of power efficiency. Typically, the devicesbeing designed by the methods outlined in this invention reduce themagnetic reluctance path by a factor of two. This reluctance reductiontranslates into a diminution of the current by the same factor and afourfold reduction in power loss.

Magnetic stimulation of neurons has been heavily investigated over thelast decade. Almost all magnetic stimulation work has been done in vivo.The bulk of the magnetic stimulation work has been in the area of brainstimulation. Cohen has been a rather large contributor to this field ofresearch (See e.g., T. Kujirai, M. Sato, J. Rothwell, and L. G. Cohen,“The Effects of Transcranial Magnetic Stimulation on Median NerveSomatosensory Evoked Potentials”,Journal of Clinical Neurophysiology andElectro Encephalography, Vol. 89, No. 4, 1993, pps. 227-234.) This workhas been accompanied by various other research efforts including that ofDavey, et al. (See, K. R. Davey, C. H. Cheng, C. M. Epstein “AnAlloy-Core Electromagnet for Transcranial Brain Stimulation”, Journal ofClinical Neurophysiology, Volume 6, Number 4, 1989, p.354); and that ofEpstein, et al. (See, Charles Epstein, Daniel Schwartzberg, Kent Davey,and David Sudderth, “Localizing the Site of Magnetic Brain Stimulationin Humans”, Neurology, Volume 40, April 1990, pps. 666-670). The bulk ofall magnetic stimulation research attempts to fire nerves in the centralnervous system.

The present invention differs in a number of respects from previousresearch efforts. First, the present invention has primary applicabilityto the peripheral nervous system, although it can be employed tostimulate nerves in the central nervous system as well. Second, and moreimportantly, the previous nerve stimulation work is dominated almostexclusively by air core coils of various shapes and sizes. The presentinvention is directed to the use of a magnetic core, more specifically apermeable core having a high field saturation, with the most preferredmaterial being vanadium permendur. Among the air core stimulators arecircles, ovals, figure eights, and D shaped coils. The coils arenormally excited by a capacitive discharge into the winding of the coreof these coils. This exponentially decaying field has a time constanttypically in the neighborhood of 100 microseconds. Typical target valuesfor the magnetic field peak happen to be near two Tesla. J. A. Cadwellis perhaps the leader among those who are now using and marketing theseair core stimulators. Among his primary patents is U.S. Pat No.4,940,453 entitled “Method and Apparatus for Magnetically StimulatingNeurons” Jul. 10, 1990. There are a number of power supplies all ofwhich operate on a basic capacitive type discharge into a number of aircore coils which are sold with his units. Various shaped coils are beingexplored at this time. One such coil is a cap shaped device which fitsover the motor cortex (K. Krus, L. Gugino, W. Levy, J. Cadwell, and B.Roth “The use of a cap shaped coil for transcranial stimulation of themotor cortex”, Journal of Neurophysiology, Volume 10, Number 3, 1993,pages 353-362).

Some efforts are being given to various circuits used to fire these aircore coils. H. Eton and R. Fisher offer one such alternative in theirpatent “Magnetic Nerve Stimulator” U.S. Pat. No. 5,066,272 Nov. 19,1991. They suggest the use of two capacitors—one to capacitivelydischarge into the coil of interest, and a second to recover the chargefrom the inductive energy resident in the coil. The circuit used in thepresent invention accomplishes the same objective with a singlecapacitor.

Some stimulation research is being performed on the peripheral nervoussystem (See e.g., Paul Maccabee, V. Amassian, L. Eberle, and R. Cracco,“Magnetic Coil Stimulation of Straight and Bent Amphibian and MammalianPeripheral Nerve in vitro: Locus of Excitation,” Journal of Physiology,Volume 460, January 1993, pages 201-219.) The bulk of Maccabee's work ishowever targeted for cranial excitation. The applications of the presentinvention focus on the peripheral nervous system although it can be usedon the central nervous system, as well.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a magnetic nervestimulator for exciting nerves of the peripheral nervous system.

A further object of the present invention is to provide a magnetic nervestimulator for non-invasive stimulation of nerves within the peripheralnervous system.

A further object of the present invention is to provide a nervestimulator for the production of magnetic fields of significant depthand focusability to stimulate deep nerves within a human.

A further object of the present invention is to provide a magnetic nervestimulator which can produce magnetic fields which can be focused oninternal peripheral nerves to effect non-invasive nerve stimulation.

A further object of the present invention is to provide a magnetic nervestimulator for the treatment of bladder and urinary disorders.

A further object of the present invention is to provide magnetic nervestimulators for the treatment of incontinence.

A further object of the present invention is to provide a magnetic nervestimulator for muscle rehabilitation and/or conditioning.

A further object of the present invention is to provide a magnetic nervestimulator for use in assisting with weight loss.

Further objects of the invention will become apparent in connection withthe disclosure provided herein.

To accomplish the objectives of the present invention, a magnetic nervestimulator is provided herein which can be used to stimulate nerveswithout the need for surgery. Magnetic stimulation of peripheral nerveshas the advantages of convenience and threshold variability overcompeting FES systems. An advance of the present invention overcompeting magnetic nerve stimulators is in the use of a highly saturablemagnetic core, i.e. a permeable core of high field saturation, and inthe design of the magnetic core stimulator itself.

In the preferred embodiment, the magnetic nerve stimulator is preferablyconstructed using a core of a magnetic or magnetizable material. Apermeable material having a high field saturation is utilized, with thepreferred core having a field saturation of at least 1.5 Tesla. Somesuitable materials for the core include vanadium permendur, orthinol,metallic glasses (metglass), permalloy, supermalloy, powdered iron, andthe silicon irons or silicon steels, in particular, 3% grain orientedsteel (magnesil). Ferrite can also be used, although it is notpreferred, due to the fact that it saturates at 0.5 T.

In accordance with the present invention, it is highly preferred that anopen core be used. Toroidal cores are not preferred, as it is has beenfound that an open core can be more effectively utilized to focus themagnetic field produced by the stimulator, and as the suitability oftoroidal cores have been found to be limited to invasive applications.By the term open core, an arc shaped core spanning an angle less than360 degrees is intended. A 180 degree core is very convenient for usingthe material efficiently since two cores can be constructed from everymandrel. A core having a larger angle (e.g. 210-220 degrees) can also beused. These cores are more focussed, although they have a smallerpenetration depth. Alternatively, cores of smaller or greater angles canbe used in non-preferred embodiments.

In the current embodiments of the invention, it is an objective to“fire” a coil having approximately a 100 microsecond characteristicdecay time, five (5) to fifty (50) times per second. The system must bereasonably efficient and reliable to fire at such a high repetitionrate. Firing rates of 5 to 10 Hz are known to be effective for treatingurinary stress incontinence using FES. Higher stimulation rates (e.g.fifty (50) Hz) have proved useful for treating irritative symptoms ofurinary frequency and urgency. Sustained contractions occur abovefifteen (15) Hz. As medical knowledge advances, various and as furtherresearch is conducted, other firing rates of higher or lowerfrequencies, or of particular excitation patterns, may prove useful inspecific applications.

The exact stimulation frequency will be varied somewhat depending on therequirements of the application in need. Sometimes muscle groups willneed to be excited for a five second period, followed by rest for a fivesecond period and then be stimulated continuously for another fiveseconds and then rest again. While they are being stimulated, it isoften desirable to have the muscle groups in a sustained contraction.This requirement dictates the necessity of continuing to pulse the coresat a repetition rate of 15 Hz. Because of the large currents involvedduring any given firing of the core, it is necessary to make the coresas efficient as possible. It is desirable to focus the magnetic fieldinto the region targeted for stimulus to the exclusion of surroundingregions. The specially designed cores offered by this invention realizethat focusability, whereas the air core coils used by the prior art donot.

With respect to the core configuration, the simplest core configurationof the present invention is that of a “C” shaped core. The span of the“C” must be carefully chosen; the span affects both the penetrationdepth and the magnitude of the field. Of additional importance is theconstruction of the core. The best cores are constructed from thinlaminate materials having a high field saturation. A typical core can bewound using two mil stock of vanadium permendur. A long ribbon of suchmaterial is wound on a mandrel (e.g. a mandrel of wood or plastic) forthe radius, thickness and depth desired. Each side of the ribbon iscoated with a thin insulative coating to electrically isolate it fromits neighbor. A generic core that might be used at various locationsaround the body can span an angle of approximately 180-220°. Once theribbon has been wound on the mandrel to the desired dimensions, it isdipped in epoxy to freeze its position. Once the epoxy has cured, themandrel is removed and the core cut for the span of angle desired. Thecut will destroy the electrical isolation of adjacent laminations. Eachcut must be finely ground so that it is smooth, and then a deep etchperformed. The deep etch is performed by dipping each of the cut ends inan acid bath. This causes the cut ends to delaminate slightly, butmaintains the electrical isolation of the laminations. Failure toperform this deep etch results in considerable eddy current loss andheating at the cut ends of the core. Following the deep etch, the endsare brushed with epoxy to maintain the shape and structural integrity ofthe core. The final step of the construction is to wind a coil ofinsulated wire about the core. A typical inductance for a core of thistype is about 30 μH. The present invention, however, may be practiced atother inductances or magnetic field strengths, as well.

In the simplest configuration, each core has only one winding. Thewinding is excited by an exponentially decaying pulse with acharacteristic time of about 100 μs. The actual signal has a ringingperiod of about that time within an envelope that is exponentiallydecaying so that only two to three cycles are ever witnessed by the coilcurrent. The excitation is repeated on a period of about approximately5-50 Hz. As stated above, the repetition cycle of these patterns will bevaried according to the application. The circuit usually consists of atransformer which feeds into a full wave rectifier bridge. The bridgevoltage charges the capacitor; the charge on the capacitor is triggeredwith a silicon control rectifier to drive current into the coil. Thereturn charge coming back through the coil the second time is fedthrough the diode back into the capacitor to prepare the circuit for thesecond phase of excitation.

There are at least three important target applications for the presentinvention—incontinence, muscle rehabilitation, and weight controltreatment. For the treatment of incontinence, it is necessary tostimulate the pelvic floor muscles. Such a stimulation is achieved byconcentrating and focusing magnetic flux directly up the vaginal cavity.One suitable core which is capable of realizing this objective isconstructed by combining two individual “C” cores each spanning an angleof about 180°. The legs of the cores are brought together in a centralregion. The common central leg of the two “C” cores is wound by a coiland the return path for the flux is split between the two “C”s. Thecores themselves fit proximally and distally under a chair which thepatient sits on during treatment.

A second area of application is in the rehabilitation of muscles. Theprimary muscle groups targeted are the thigh, calf, biceps, and triceps.The geometry is similar for all these applications, and thus acylindrical extension around the muscle is used. Although one solutionfor this problem is a simple “C” core and coil which is moved around bythe discretion of the patient, an alternative stimulator resembles thetubular shape motors used in electromechanics to propel a secondarymember down a tube. Here the geometry would necessarily require a hingedtubular shape having recesses or slots which would run azimuthallyaround the muscle group to be stimulated. The coils of the stimulatorfits in these recesses or slots and the surrounding structure wouldagain be a laminated vanadium composite. If the structure were fittedwith two or three coils, they could be stimulated in a phasedarrangement.

Such an excitation would have the effect of kneading the muscle tissuegroup along its longitudinal axis. This particular excitation patternmay be instrumental in more fully recruiting larger muscle groups suchas the hamstring group in the leg. Full recruitment or stimulation ofthe nerve group would be advantageous to long term rehabilitation.Preliminary experiments with the device indicate that excitations at thefrequencies mentioned accomplish exercise of the muscles at a higherefficiency and rate than could be accomplished through normal means.

Another area of application is that of assisting in weight lossmanagement. As with muscle rehabilitation, one alternative is to simplyuse a handheld unit moved over multiple areas of the body. One groupwhich can be particularly difficult to stimulate is the abdominal wall.An alternative method for realizing excitation of this group resembles achest plate which can be secured to a patient or hinged to the side of achair in which the patient sits. The chest plate contains a two or threephase arrangement of coils backed by the high field saturation coresconstructed in the manner dictated above. The cores are spaced to drivethe flux deeply within the abdominal muscle group. Both in musclerehabilitation and in weight loss management, the phasing of the coilscan be alternated with time to give the effect of a back and forth“kneading” stimulation pattern. The rationale behind weight managementis that the firing of these muscle groups requires the uptake ofadenosine triphosphate; this energy expenditure is being artificiallyinduced by the magnetic stimulator.

In summary, it is noted that there are a number of ways to moreefficiently stimulate various muscle groups within the body. The key tothese more efficient techniques revolves around using a thin laminatematerial of high magnetic field saturation to construct these cores andthereby drive and focus the flux into the regions desired. A simple “C”type core achieves a reluctance advantage of at least a factor of twoover conventional cores. By using multiple cores connected at a centerleg, a single focus site can be achieved with the return path disbursedin two or more areas so as to discourage excitation when the field isreturned. In other applications, multiphased coils that actually enclosethe tissue of interest can be excited so as to roll or knead musclegroups directionally with time. Certain wrapping applications may bemore instrumental for higher recruitment of injured muscle groups.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a “C” shaped core stimulator with the toroidalcoil field winding wrapped around the core. The field lines (dotted)indicate the depth of penetration and focusing of the stimulation.

FIG. 2 is a schematic of the electrical circuit used to stimulate thecoil winding.

FIG. 3 is a side view of a core stimulator configuration used in thetreatment of incontinence; the core is designed to fit underneath a seatwhich the patient sits on during treatments.

FIG. 4 is a perspective view of a core stimulator (wrapped around apatient's leg) used to massage muscles in the leg for rehabilitationpurposes. The tubular core is hinged on one side and is designed to foldaround the leg.

FIG. 5 is a perspective view of a half section of the core stimulatorused for arm or leg muscle rehabilitation; windings of different phasesare placed in adjacent recesses or slots, cut into the core.

FIG. 6 is an end view of the leg or arm stimulator. The winding goingfrom one section to the next is taken out in a long fold to allow forease of opening of the core units for facilitating placement around theleg or arm.

FIG. 7 is a schematic perspective view of a hinged multiphasedstimulator designed to conform around the torso of the patient.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS

In accordance with the present invention, a magnetic nerve stimulator isprovided which can be used for non-invasive stimulation of nerves in theperipheral nervous system. The advantage of non-invasive stimulation isa significant one, as nerves can be stimulated deep beneath the surfaceof the skin without the necessity for surgery, incisions in the body, orthe use of uncomfortable electrodes. To achieve an effectivenon-invasive stimulator, however, the stimulator must be carefullydesigned to achieve sufficient depth and penetration within the body soas to effectively stimulate the nerves or nerve groups of interest.

The present inventors have recognized the objective of highly effectivenon-invasive stimulation by providing a magnetic nerve stimulator whichcan achieve significant depth and penetration, such that internal humannerve groups can be stimulated to treat incontinence, achieve musclerehabilitation (or conditioning) or assist with weight loss.

In the preferred embodiment, the core is constructed out of a permeablemagnetic material having a high field saturation. By high fieldsaturation, the inventors refer to the fact that a magnetizable materialis utilized which saturates at 1.5 Tesla or higher.

The magnetic nerve stimulator is preferably made with a magnetizablematerial. Since the magnetic fields desired typically reach 1.5 Tesla orhigher, it is desirable to use materials which saturate at or above 1.5Tesla. One suitable material, for example, is vanadium permendur. Othersuitable materials include the metallic glasses (i.e. metglass),permalloy, supermalloy, powdered iron, and silicon irons or siliconsteels, in particular, 3% grain oriented steel (magnesil). Ferrite canalso be used, although it is not preferred, due to the fact that itssaturates at 0.5 T. These materials can be obtained, for example, fromMagnetics, Inc. in Butler, Pa.

It has been found that 3% grain oriented silicon steel is a particularlyuseful core material. This material has the advantage of providing verygood performance at a relatively low cost. Grain oriented steel is alsouseful since it can be wound on a bobbin. A higher field can be reachedwhen the magnetic grains are oriented azimuthally (around the bobbin) inthe direction that the field will travel.

A summary of some materials which can be used for the core and theircharacteristic properties is as follows:

TABLE I Materials for the Magnetic Core Material Frequency SaturationPermendur <5 kHz 2.2 T Magnesil (3% grain oriented <1 kHz 1.75 T steel)Powdered iron <10 kHz 1.75 T Metglass <100 kHz 1.5 T Orthinol <10 kHz1.45 T Permalloy >10 kHz 0.7 T Supermalloy >10 kHz 0.7 T Ferrite <500kHz 0.5 T

Thus, in general, the use of a magnetizable material is preferred forthe core as it helps to focus and enhance the magnetic field used fornerve stimulation. Accordingly, materials with a high field saturation,i.e. materials saturating at 1.5 Tesla or higher, are recommended. Withsome materials, a saturation of 2.0 Tesla can be achieved. Although, inaccordance with the disclosure herein, magnetic nerve stimulators canalso be constructed using materials which saturate at lower fields, forexample, materials which saturate at 1.0 Tesla or higher, or even at 0.5Tesla or higher, such as ferrite. These stimulators are not preferred,however, as they have been found to be less effective.

In accordance with the present invention, the use of an open core isdesirable as well. By the term “open core”, the inventors refer to thefact that the core is curved into an arc such that there is a gap oropening between the ends of the core. This enables the magnetic fieldgenerated by the core to be more strongly and precisely focussed beyondthe opening and therefore, beneath the surface of the skin. Thus, anopen core is used to provide a desirable degree of penetration andfocussing and thereby improve the stimulator's effectiveness.

The open core is non-toroidal, i.e. it spans an arc of less than 360degrees, with a gap between the ends of the core. In the preferredembodiments, the open core is C-shaped. A preferred angle for the spanof the arc of the core is approximately 180-220 degrees. In thepreferred embodiments, a suitable core can span an angle fromapproximately 205 to approximately 215 or 220 degrees. In otherembodiments, cores of approximately 190-230 degrees can be utilized.Alternatively, a core spanning an arc of approximately 180-270 degreesare also possible. The greater the arc angle, the better the fieldfocussing, however, the penetration depth is lower. Unless the geometrydemands it, there is believed to be no advantage to a core spanning anangle less than 180 degrees.

A large radius is also recommended for the core to stimulate deepnerves. The magnetic field falls off exponentially as the inversedistance between the pole heads. A small radius core has a very highfield between the heads, but the field falls off rapidly. A large corehas a lower field between the heads, but the field falls off lessrapidly. Thus, the larger radius core will have a higher field a fewcentimeters into the body. For incontinence treatment, it is desired tostimulate the pelvic floor muscles. A penetration depth of at least 5 cmfor this task is recommended, and thus a larger radius core ispreferred. Placing two (2) cores together has the advantage ofconcentrating the field in one point. The field is cut in half at thereturn points. This discourages secondary stimulation sites. For ahandheld device, an outer diameter of approximately 5″ and an innerdiameter of approximately 4″ is recommended. For the incontinencedevice, an outer diameter of approximately 6″ and an inner diameter ofapproximately 3″ is recommended. For the coil, 15 kVolt No. 6 AWG wirewith 15 kV insulation can be utilized.

The present device yields much greater stimulus for the same current asprior art devices, which is a significant improvement in performance.One test of the device, for example, demonstrated nearly twice thestimulus over a well known prior art device, for the same amount ofcurrent.

Another important advantage of the present invention is that the designof the stimulator allows magnetic treatment to be external. By“external”, the present inventors refer to the fact that stimulation canbe achieved without implantation of any elements within the body, orengaging in any surgery or surgical incision. Thus the use of aninternal element of any sort in the human body, such as, for example, animplanted electrode, is not necessary. The high field saturationmaterial used in the stimulator provides a magnetic field of sufficientdepth and focusability to effectively penetrate the organism andstimulate the internal nerves within the organism without the need forany invasive surgery. This is a particularly great advantage in thetreatment of incontinence. It is also of potential usefulness in otherapplications as well.

As shown in FIG. 1, a “C” shaped core is disclosed which is capable ofstimulating various peripheral nerve groups throughout the body. Thecore 2 is constructed by winding two to four mil laminations of amaterial having a high magnetic field saturation on a mandrel; thenumber of laminations required will be dictated by the thickness anddepth of the core desired.

This closed loop spool of laminations is removed from the mandrel andcoated with epoxy to give the unit structural integrity. The closed loopis then cut to give the length and angle of the “C” shape, as desired. Adeep acid etch is then performed on the cut edges. The cut edges aresoaked in an acid bath which causes the epoxy to dissolve resulting in aslight delamination of the core in the vicinity of the cut. Epoxy isthen brushed on the etched ends to prevent further delamination. Thisprocedure is necessary to prevent eddy currents from flowing in thecore. This would diminish the effective B field which can be produced bythe core.

The laminate material should be constructed of a saturable material, andpreferably a material having a high field saturation. As previouslydescribed, the characteristic magnetic fields in the cores havepreferred strengths of at least 1.5 Tesla. With suitable materials,characteristic fields in the range of at least two Tesla can beachieved. Preferably, vanadium permendur or 3% grain oriented steel isused, as these materials carry a high field density, although thepresent invention is not limited to those preferred embodiments. In thepresent stimulators, high field saturation is more important than highpermeability.

In addition to the factor of high saturation, it can also be desirablein preferred embodiments to choose the core to minimize heat productionand/or to minimize noise levels. In particular, minimization ofhysteresis losses is desirable. Hysteresis is internal loss due to achange of orientation of the molecular structure of the core material.This is related to how open the BH loop is. Hysteresis is probably thechief contributor to the heating in the core. When an applied fieldchanges the length of the material, the material is referred to asdisplaying magnetorestriction. This can result in noise during thestimulator's operation. Eddy current losses can be addressed by usingsmall thickness stock or even powder.

One useful material to achieve low hysteresis losses and lowmagnetorestriction are the supermalloy products. These materials have ahigh nickel content (50%-80%). The 80% nickel variation has very lowhysteresis losses, although the material saturates at only 0.7 T. Thesenickel alloys can be obtained in half mil thicknesses.

Another material which can be used is metglass. This is a metalizediron-glass material with low internal resistance. The normal materialhas a trade name of NAMGLASS1 or SA1. This material can be transversefield annealed. This process orients the grain structure at right anglesto the field flow use. The annealing lowers the hysteresis losssignificantly. It also lowers the permeability, although that effect isnot of significance for the purposes of the present stimulator. Thematerial also has very low magnetorestriction.

Another material, pure iron, is very soft and has a rounded loop. Thisductility is believed to reduce the noise. It saturates at 1.7 T and isoften found in powdered cores.

As noted above, another useful material for the core, in general, is 3%grain oriented steel. A generic name for this material, which is used bysome manufacturers, is magnesil. The material is essentially steel with3% silicone, and saturates at 1.75 T. Another suitable material for thecore is supermendur. This material includes iron and cobalt andsaturates at 2.2 T. Both of these materials, however, are highlymagnetostrictive, changing length when exposed to a magnetic field. Bothmaterials also have a square BH loop.

After choice of the core, a winding or coil 4 is then wrapped around thecore in such a way as to drive the flux through the cut ends 5. Thefield lines 6 give an indication of the depth of penetration and degreeof focusing expected with such a core.

FIG. 2 shows an electrical circuit used to “fire” the core and coil ofFIG. 1. A normal 120 volt, 60 Hz signal excites the circuit at 7. Atransformer 8 amplifies the voltage up to about 1-3 kV. This highvoltage AC signal is then fed into a full wave rectifier bridge 10. Thesignal from the rectifier bridge is then passed through a diode 12 tocharge a capacitor 14. The purpose of all the electrical components tothe left or upstream of the capacitor is to simply put charge into thecapacitor. The energy residing in the circuit which will be pumped intothe stimulator core is one-half C (the capacitance value) times thevoltage squared. When thyrister 16 is triggered with a small controlvoltage pulse, current flows through the thyrister and into the core 2.Most of this energy goes back into the capacitor 14, recharging it inthe opposite polarity from its initial charge. The reverse chargedcapacitor 14 immediately discharges again through the stimulator coil 2through diode 18, connected in parallel. Theoretically, all of thisenergy should pass into capacitor 14 to recharge it according to itsinitial polarity. In practice, of course, this LC circuit has some loss,and the thyrister 16 does not shutoff immediately. Two to threeexponentially decaying ring cycles of this L circuit are witnessed inpractice before current of core 2 is completely shut off. After shutoff,the capacitor charges through diode 12 as it did initially. It continuesto charge until thyrister 16 is triggered again.

Different stimulation/rest cycles are employed for different tasks. Inthe treatment of incontinence, one such stimulation cycle might be fiveseconds on, five seconds off. During the five seconds which arecharacterized as “on”, thyrister 16 could continuously be pulsed 15times per second. These stimulation montages can be altered according tothe requirements and goal of the stimulation protocol.

The circuit shown is a preferred embodiment for the practice of thisinvention but other circuit designs (such as a dual capacitorarrangement or so forth) may be used to fire the coil as well, as willbe apparent to those skilled in the art. Moreover, whereas the magneticfield produced by this embodiment pulses at approximately 20-50 kHz,variations in that frequency may be practiced as well. This frequency issimply:

1/2π{square root over (LC)}  (Equation 1)

Shown in FIG. 3 is a dual “C” core type arrangement suitable for thetreatment of incontinence. The individual “C”s comprising this core eachspan an angle of about 220°. The cores 20 are placed end to end in a Wtype arrangement. The winding 4 is wrapped around the common center legof the two cores. The cut ends of these cores are designed to be flushwith the lower side of a saddle cushion 21 in which the patient sits.The primary flux is driven up the common central core into the vaginalcavity. This flux is returned through the posterior and anterior arms ofthe “W”. Because the return flux is much lower in magnitude, nostimulation occurs except at the vaginal floor near the center leg ofthe “W”.

FIG. 4 shows a core stimulator suitable for exciting leg and arm musclegroups. In this configuration the cores 22 would constitute a tubulartype shroud into which a leg 24 or an arm would be inserted. Althoughthe “C” core of FIG. 1 would be suitable for this task, its geometry isdifficult to achieve a homogenous and controlled stimulus of this musclegroup. As shown in FIG. 5, each section of the stimulator 22 iscomprised of two half shells 26. Recesses or slots 27 are cut into thehalf shells to allow placement of coils which will be woundpreferentially within the shells. The individual windings of the shell26 are aligned in such a way as to create a magnetic field which ispreferentially along the axis of the arm or the leg. Adjacent recessesor slots of the stimulator 22 will contain different phases. A two orthree phase arrangement is used to excite a traveling magnetic fieldwhich moves down and up the axis of the arm/leg. This windingarrangement is not unlike that used in tubular motors to realize anaxial traveling wave. One edge of the two common halves constituting thestimulator 22 must act as a hinge. The winding electrically connectingthe two halves is simply accomplished by bringing the wire down as anextension 28 as suggested in FIG. 6. The extra length of windingassociated with the extension 28 guarantees the needed flexibility ofthe stimulator to hinge and wrap around the patient's arm or leg.

FIG. 7 suggests yet another alternative embodiment suitable for thestimulation of abdominal muscles. Here the stimulator 30 is hinged to achair into which the patient sits. The stimulator then folds around thepatient's abdomen during treatment. The stimulator 30 is againconstructed of laminated permeable material having a high magnetic fieldsaturation. Multiple windings are laid in recesses or slots which arecut into the core. The windings are designed to drive flux into theabdomen and cause a contraction of the abdominal wall muscle group.Again the windings can be phased to cause a directional massaging ofthis muscle group.

Having described this invention with regard to certain specificembodiments, it is to be understood that the description is not meant asa limitation since further modifications may now suggest themselves tothose skilled in the art and it is intended to cover such modificationsas fall within the scope of the appended claims.

We claim:
 1. An apparatus comprising: a magnetic nerve stimulatorcomprising a seat; and two C-shaped cores in proximity to one another toform a common leg portion, said cores being located beneath said seat,wherein said magnetic nerve stimulator directs a magnetic field into theanatomy of the user when the user is sitting on said seat and stimulatesnerves of the user.
 2. An apparatus as claimed in claim 1, wherein saidcores of said magnetic nerve stimulator are adapted to stimulate nerveswhich cause contraction of the bladder muscles of the user.
 3. Anapparatus as claimed in claim 1, wherein said magnetic nerve stimulatorcomprises a core of magnetic material.
 4. An apparatus as claimed inclaim 3, wherein said core is located beneath said seat.
 5. An apparatusas claimed in claim 1, wherein said magnetic nerve stimulator comprisesa core of highly saturable magnetic material, said highly saturablemagnetic material comprising a magnetizable material which saturates atmagnetic fields of at least 1.5 Tesla.
 6. An apparatus as claimed inclaim 1, wherein said magnetic nerve stimulator comprises a core ofhighly saturable magnetic material, said highly saturable magneticmaterial comprising a magnetizable material which saturates at magneticfields of at least 2.0 Tesla.
 7. An apparatus as claimed in claim 1,wherein said seat is part of a chair.
 8. An apparatus as claimed inclaim 3, wherein said magnetic nerve stimulator comprises a stimulatorcoil for carrying electrical current in proximity to said core, andelectric current means connected to said stimulator coil to create anelectrical current flow in said stimulator coil and cause saidstimulator coil and said core to generate a magnetic field.
 9. Anapparatus as claimed in claim 3, wherein said magnetic materialcomprises a silicon steel.
 10. An apparatus as claimed in claim 3,wherein said magnetic material comprises 3% grain oriented siliconsteel.
 11. An apparatus as claimed in claim 9, wherein said siliconsteel is wound on a bobbin.
 12. An apparatus as claimed in claim 9,wherein said silicon steel comprises magnetic grains, and wherein saidmagnetic grains are oriented azimuthally in the direction that saidmagnetic field will travel.
 13. An apparatus as claimed in claim 3,wherein said magnetic material comprises a metallic glass.
 14. Anapparatus as claimed in claim 13, wherein said metallic glass istransverse field annealed.
 15. An apparatus as claimed in claim 3,wherein said magnetic material comprises orthinol.
 16. An apparatus asclaimed in claim 3, wherein said magnetic material comprises permalloy.17. An apparatus as claimed in claim 3, wherein said magnetic materialcomprises vanadium permendur.
 18. An apparatus as claimed in claim 3,wherein said magnetic material comprises powdered iron.
 19. An apparatusas claimed in claim 3, wherein said magnetic material comprisessupermalloy.
 20. An apparatus as claimed in claim 3, wherein saidmagnetic material comprises ferrite.
 21. An apparatus as claimed inclaim 1, wherein said magnetic nerve stimulator comprises: (a) an opencore; (b) a stimulator coil for carrying electrical current in proximityto said core; and, (c) electric current means connected to saidstimulator coil to create an electrical current flow in said stimulatorcoil and cause said stimulator coil and said core to generate a magneticfield.
 22. An apparatus as claimed in claim 1, wherein said magneticnerve stimulator comprises: (a) an open core of highly saturablemagnetic material, said highly saturable magnetic material comprising amagnetizable material which saturates at magnetic fields of at least 1.5Tesla; (b) a stimulator coil for carrying electrical current inproximity to said core; and, (c) electric current means connected tosaid stimulator coil to create an electrical current flow in saidstimulator coil and cause said stimulator coil and said core to generatea magnetic field.
 23. An apparatus as claimed in claim 1, wherein saidmagnetic nerve stimulator comprises: (a) an open core of highlysaturable magnetic material, said highly saturable magnetic materialcomprising a magnetizable material which saturates at magnetic fields ofat least 2.0 Tesla; (b) a stimulator coil for carrying electricalcurrent in proximity to said core; and, (c) electric current meansconnected to said stimulator coil to create an electrical current flowin said stimulator coil and cause said stimulator coil and said core togenerate a magnetic field.
 24. An apparatus as claimed in claim 21,wherein said open core spans an angle of approximately 180 to 270degrees.
 25. An apparatus as claimed in claim 21, wherein said open corespans an angle of approximately 190 to 230 degrees.
 26. An apparatus asclaimed in claim 21, wherein said open core spans an angle ofapproximately 205 to 220 degrees.
 27. An apparatus as claimed in claim22, wherein said open core spans an angle of approximately 180 to 270degrees.
 28. An apparatus as claimed in claim 22, wherein said open corespans an angle of approximately 190 to 230 degrees.
 29. An apparatus asclaimed in claim 22, wherein said open core spans an angle ofapproximately 205 to 220 degrees.
 30. An apparatus as claimed in claim23, wherein said open core spans an angle of approximately 210 to 270degrees.
 31. An apparatus as claimed in claim 23, wherein said open corespans an angle of approximately 190 to 230 degrees.
 32. An apparatus asclaimed in claim 23, wherein said open core spans an angle ofapproximately 205 to 220 degrees.
 33. As apparatus as claimed in claim3, wherein said core has cut ends and said seat has a lower side, andwherein said cut ends are flush with said lower side.
 34. An apparatusas claimed in claim 1, wherein said cores of said magnetic nervestimulator are adapted to direct said magnetic field into the vaginalcavity of a female user.